The role of angiogenesis in hematologic malignancies

Anti-VEGF Drugs in the Treatment of Multiple Myeloma Patients

The interaction between the bone marrow microenvironment and plasma cells plays an essential role in multiple myeloma progression and drug resistance. The vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR) pathway in vascular endothelial cells activates and promotes angiogenesis. Moreover, VEGF activates and promotes vasculogenesis and vasculogenic mimicry when it interacts with VEGF receptors expressed in precursor cells and inflammatory cells, respectively. In myeloma bone marrow, VEGF and VEGF receptor expression are upregulated and hyperactive in the stromal and tumor cells. It has been demonstrated that several antiangiogenic agents can effectively target VEGF-related pathways in the preclinical phase. However, they are not successful in treating multiple myeloma, probably due to the vicarious action of other cytokines and signaling pathways. Thus, the simultaneous blocking of multiple cytokine pathways, including the VEGF/VEGFR pathway, may represent a valid strategy to treat multiple myeloma. This review aims to summarize recent advances in understanding the role of the VEGF/VEGFR pathway in multiple myeloma, and mainly focuses on the transcription pathway and on strategies that target this pathway.

Emerging strategies for targeting cell adhesion in multiple myeloma

Multiple myeloma (MM) is an incurable hematological cancer involving proliferation of abnormal plasma cells that infiltrate the bone marrow (BM) and secrete monoclonal antibodies. The disease is clinically characterized by bone lesions, anemia, hypercalcemia, and renal failure. MM is presently treated with conventional therapies like melphalan, doxorubicin, and prednisone; or novel therapies like thalidomide, lenalidomide, and bortezomib; or with procedures like autologous stem cell transplantation. Unfortunately, these therapies fail to eliminate the minimal residual disease that remains persistent within the confines of the BM of MM patients. Mounting evidence indicates that components of the BM-including extracellular matrix, cytokines, chemokines, and growth factors-provide a sanctuary for subpopulations of MM. This co-dependent development of the disease in the context of the BM not only ensures the survival and growth of the plasma cells but contributes to de novo drug resistance. In addition, by fostering homing, angiogenesis, and osteolysis, this crosstalk plays a critical role in the progression of the disease. Not surprisingly then, over the past decade, several strategies have been developed to disrupt this communication between the plasma cells and the BM components including antibodies, peptides, and inhibitors of signaling pathways. Ultimately, the goal is to use these therapies in combination with the existing antimyeloma agents in order to further reduce or abolish minimal residual disease and improve patient outcomes.

Infliximab chimeric antitumor necrosis factor-α monoclonal antibody as potential treatment for myelodysplastic syndromes

Accumulating evidence indicates tumor necrosis factor-a (TNF-a) as a key cytokine in the pathogenesis of the myelodysplastic syndromes (MDS). The identification of TNF-a as a regulator of apoptosis and the increased susceptibility of MDS cells to this cytokine provided the basis for several clinical trials of TNF inhibitors. Infliximab is an IgG1 chimeric anti-TNF-a monoclonal antibody composed of human constant and murine variable regions that bind specifically to both soluble and membrane-bound TNF-a. To date, only 2 studies have investigated the use of infliximab in patients with low-risk MDS. In both reports the drug showed a limited but significant activity and a favorable side-effect profile. In some patients, hematopoietic response was associated with decreased apoptosis as well as a decrease in abnormal metaphases by 50%. Further studies are currently underway and should provide useful information to define the more responsive subtypes of MDS, the patient characteristics, and the proper dosing regimen.

Tumor angiogenesis in the bone marrow of multiple myeloma patients and its alteration by thalidomide treatment

Angiogenesis in solid tumors is important to tumor growth, invasion and metastasis. Recently, it has been suggested that angiogenesis plays a certain role in the development of hematopoietic malignancies, including leukemia and multiple myeloma. We evaluated tumor angiogenesis in the bone marrow (BM) of multiple myeloma (MM) patients by calculating microvessel density (MVD) in needle-biopsy specimens obtained from 51 cases of untreated MM or monoclonal gammopathy of undetermined significance (MGUS). The MVD in the BM of donors for transplantation and patients with non-hematological diseases was calculated as a control. There was an obvious increase in MVD in the BM of MM patients, and the MVD correlated with the grade of myeloma cell invasion of the BM in the untreated MM cases. It was recently reported that thalidomide might be effective for the treatment of MM. We assessed the effect of thalidomide on angiogenesis in BM treatment of 11 patients with refractory MM. The concentration of M-protein in the serum or urine of seven of the 11 patients was reduced by at least 30% after thalidomide treatment, and MVD in the BM decreased in three of these seven cases in response to thalidomide. Increased plasma concentrations of basic fibroblast growth factor (FGF-2) and vascular endothelial growth factor (VEGF) were observed in all 11 cases before thalidomide administration and both levels were reduced after treatment with thalidomide. Augmented angiogenesis in the bone marrow of MM patients was confirmed in the present study. It seems that thalidomide is effective in the treatment of MM through the impairment of angiogenesis by decreasing FGF-2 and VEGF production. This is the first report on pathological evidence in the bone marrow of MM before and after thalidomide treatment, in Japan.

[Therapy-related changes of angiogenesis in Philadelphia chromosome positive chronic myelogenous leukemia]

To elucidate the effect of first-line treatment with interferon (IFN), hydroxyurea (HU) and the tyrosine kinase inhibitor imatinib (STI571) on angiogenesis, we studied bone marrow (BM) biopsies in 104 patients with chronic myelogenous leukemia (CML) and 138 patients before and after allogeneic BM transplantation (BMT). After immunostaining (CD34) and morphometric analysis in comparison with a control group, CML specimens showed an increased vascularity and conspicuous morphological abnormalities of microvessels. A close relationship between microvessels and fiber density was detectable in initial biopsies and also in repeatedly performed examinations following therapy. Monotherapy by imatinib and HU generated a significant reduction of microvessels and reticulin fibers in contrast to changes after IFN administration or combination regimens of IFN and HU. A persistence of numerical and structural anomalies of vasculature was observable even several months after BMT. These anomalies shed some light on disturbances of the stroma compartment after myeloablative therapy. The relationship between BM vascularity and fibers is probably dependent on concomitant changes of megakaryopoiesis as the source of various mediators involved in the development of myelofibrosis and neo-angiogenesis acting within a complex functional network.